Resistance thermometer



March 30, 1943. w. o. UNCE M. T% m 01 M. mm.

. 3 OH. I EN C0 N Ad v wk 5 2 I l I F 6 March 30, 1943. w. D. MOUNCE 2,315,127

' RESISTANCE THERMOMETER Filed Oct. 12, 1939 [2 Sheets-Sheet 2 4 12' 9 24 Mimi FIG. 2. FIG. 3

mama/nee INVENTOR.

I ATTORNEY.

Patented Mar. 30, 1943 RESISTANCE TnEnMoMirrEn Whitman D. Mounce, Houston, Tex., assignor to Standard Oil Development Company, a corporation of Delaware Application October 12, 1939, Serial No. 299,666

6 Claims.

to provide a bore hole thermometer in which.

power may be supplied to the measuring unit in the form of alternating current and in which direct current provides the temperature indication.

In my copending application Serial No. 167,965 I have disclosed an electrical bore hole thermometer in which a bare conductor of low heat capacity is usedas the measuring unit. This measuring unit is connected to a transformer which, in turn, is electrically connected to a source of alternating current by a circuit containing a cable,so that the measuring unit may be lowered into a bore hole while the source of current remains at the surface of the earth. Changes in temperature of the 'measuring unit cause changes in the impedance of the alternat ing current circuit and so enable an indication of the temperature of the measuring unit to be obtained at the surface of the earth.

While the thermometer described in my copending application has a high sensitivity, low

heat capacity and high thermal conductivity, there' are limits to its usefulness. Due to the fact that transformers otherwisesuitable for use in this device have temperature coefiicients comparable to that of the measuring element in addition to a high heat capacity and-aj'low -thermal conductance compared to that 'of the element, serious errors in the measurement of the actual temperature result. This occurs as a drift in the recorded measurement.

ance thermometer which does not possess the limitations of the thermometer described'in copending application Serial No. 167,965, but which retains all of its advantages. In addition, it may be modified to make differential temperature In addition, when the instrument is used at high sensitivity on a single casing 3. The purpose of this arrangement is to measurements, a. characteristic which is often useful and which is not possessed by my previously described thermometer.

The present application is directed to a bore hole thermometer in which a branch or branches of an alternating current bridge form the temperature measuring unit. Changes in the temperature of the temperature measuring unit changes its impedance which, in.turn, changes the amount of current flowing across the bridge, and this current flowing across the bridge is rectified to direct current and used to indicate the temperature of the measuring unit.

Other objects and advantages of the present invention may be seen from the following description taken in conjunction with the drawings in which Y Fig. 1 is a front elevation of a modification of the invention, as applied to a bore hole, with a portion of the apparatus broken away to reveal interior construction;

Fig. 2 is a front elevation of a modification of the invention in which two measuring units are exposed so that the reading obtained will be in terms of temperature variation rather than actual temperature; and

. Fig. 3 is a diagrammatic illustration of a circuit which may be substituted for the circuit used in the devices shown in Figs. 1 and 2.

.Referring'to Fig. l in detail, numeral i designates a section of the earth penetrated by bore hole 2. Within the bore hole is a casing 3 which may be of any desired form and is shown in the drawings as a cylindrical bomb composed of Bakelite or other insulating material. Arranged in circumferential groove 4 of casing 3 is a strip of metallic material 5 which may be copper, platinum, nickel or any other good conductor of heat or electricity. As shown ,in' the drawings,-

this conductor is of a thickness such that the outer surface lies flush .with the outer surface of subject the exposed surface of the conductor strip to the abrasive action of the mud employed in drilling and thereby prevent the accumulation on the conductor of any chemical film which would retard the rate of heat transfer from the fluid to the element.

Supported within casing 3, in a suitable manner, is a transformer 6 having a primary winding 1 and a secondary winding 8. One end of primary winding 1 is connected to conductor 9 contained within a cable It) while the other end of winding 1 is attached by conductor ii to the metal electrode l2 which forms a tip for casing 3.

con uctor I! by means of a slip ring HO. Gon- 5 ductor It connects to one end of winding ll of transformer l1, the other end of this winding being connected toan electrode i. which is stuck into the surface of the earthvat the bore hole. The other winding I! of transformer ll is connected to a source of alternating current of constant ire uency, such, for example. as a very constant speed generator or vacuum tube oscillator. Inserted in conductor "is a condenser 2| and attached to conductor I! on either side of condenser circuit, being connected across from the juncture of resistances and 26 to the juncture of resistances Sand 21 by means of. conductors 2|.

One end of secondary winding 2| or transformer 29 is-connected to conductor" by means of conductor 32. The other end of secondarywinding 3| is connected by conductor 32 to the conductor l in cable Ill. Inserted in conductor 23 is a rectifier 34 and resistances 35 and It. A condenser 21 has one plate connected to conductor 32 and its other plate connected to conductor 33 between rectifier and resistance 35, .while a second condenser. 28 has one-"plate connected to conductor 32 and itsother plateconnectedto conductor 32 between resistances 3i and 28. Another condenser 29 is inserted in conductor ll between to separate the alternating current transmitted 1 in Fig. 2 is particularly valuable in logging wells to the device from the direct current signal.

In the modification of thelnvcntion shown by Fig.2 the same electrical 'circuit'isused as in Fig. 1-. -Ira-this modification, however, the two resistances S and 25 of the alternating current bridge aree p fi to the drilling. fluid. This modification of the invention is used to measure changes in the temperature gradient rather than the actual temperature in the bore hole. 7

Fig. 3 is a diagram of an electrical circuit which may be substituted for the electrical 011'? cuitusedin Fig. 1. In themodiflcation shown; in this figure, an electrical rectifier 40 anda vac- -uum tube 4| are-used to rectify and amplify the signal produced by current flowingacross the alternating current bridge. As will be seenirom no 7 or my invention, it will be obvious to a skilled this diagram, secondary winding I of transformer 6 is connected not only to electrical bridge 23, but also by leads 42 to the filament Q3 of vacuum tube ii in order to produce the power for operating the vacuum tube. 5

It will be seen that, when using electrical rectitier 40 and vacuum tube ll in'the circuit, it is necessary to use condensers'andresistances in a somewhat diil'erent manner in order to obtain optimum-results than they are used in the modification by'l ig. 1. In Fig. 3 the conductor lj-which connects one lead of the secondary of transformer]! to conductor} contains a condenser choke 38 and rectifier 4. and, in

addltion,isconnected tothe'plate ofvacuumtuhe thus described and illustrated, what is-f ll at a point between the condenser and the choke coil. The other lead of the secondary of a transformer 20 is connected through variable resistance I to thegrid of vacuum tube 4| by con ductor ll. Across conductors 23 and ll is connected condenser 41, resistance 4| and resistance 02. In cable I between its Junction with conductor 23 (and transformer 6 is placed condenser 16*. In the modification shown by Fig. 1 as the casing 2 is lowered into a bore hole filled with. fiuid, the impedance of metallic strip I changes as the temperature of the fiuid inthe bore hole changes. This change in impedance causes the i5. balance of electrical bridge to change and so causes a variation in the amount o1 direct current sent through the rectifier and up the cable II. In operating this device, I prefer to adjust the resistances-composing electrical bridge 22 so go that the resistance of unit 5 is slightly greater than that of unit 28 producing a slight unbalance oi the bridge. The. temperature increases as the 'device is lowered in the bore hole, causes the bridge to become increasingly unbalanced and the 5 direct: current signal to become increasingly great.

In the modification shown in Fig. 2 the resistance I forms 'one arm of the alternating current bridge, while resistance 25 forms the other arm.

30 Since both oi these resistances are constructed of the same material and with substantially the I same dimensions, as the temperature of the bore hole gradually increases, the impedance of both of these resistances will increase together and the all changes will tend-to cancel out each other. However, if there is a sudden ,variation'of temperaiurein the bore hole, the temperature of strip 5 will be difierent from that of strip 25, causing the 1 balance or the bridge to change which, in tum, causes the direct current which produces the tem- Jg? perature signal also to change. By the use of this arrangement only variations in the temperature from the general temperature gradient of the bore hole will be observed. The device shown because it is not so much the actual temperature of'the hole that is desired, but the points in the 1 hole where there are noticeable temperature variatlons. so The device shown in Fig. 3 may be substituted t for the measuring circuit'used in either Figs. 1 or 2. By the use of a vacuum tube, rectifier and mplifier better results are obtained than with the use of the copper oxide rectifier generally used 5; in the circuit shown in Figs. 1 and 2. While in Fig. 3 only resistance 5 is shown as a variable resistance as inFig. 1, it is apparent that both "the modification in Fig. 2.

' While I have described preferred modifications may befimade without departing from the in-i vention. t

The nature and cbiects of the invention having resistances 5 and 25 maybe variable as shown by means for converting the changes in said alternating current due to changes in the temperature of said exposed conductive element into direct current voltages whereby the latter may be' transmitted to the surface by the same means which carries the alternating current from the surface.

2. A device for measuring temperature variations in a fluid in a bore hole comprising a bomblike casing attached to the end of a cable adapted to raise and lower said casing in the bore hole, an

electrical bridge in said casing comprising four resistances of two arms of said bridge are arranged for direct heat exchange with the fluid arms, each containing a resistance, one of said resistances being a conductive element exposed to the fluid in the bore hole and responsive to tem- "perature changes in said fluid, a first and second transformer having primary and secondary windings, electrical connections between the secondary of the first transformer and two opposite junctions of said electrical bridge, electrical connections between the primary of the second transformer and two other junctions of said electrical bridge, a conductor carried by said cable for supplying alternating current to the primary of the first transformer, a second conductor including a rectifier connecting the secondary of the second transformer to said first conductor, a condenser in said first conductor b tween the point of con nection of said second conductor therewith and the primary of said first transformer, a source of alternating current connected to said first conductor, and means for measuring the rectified current and adapted to be located-at the top of said bore hole connected to said first conductor.

,3. A device according to claim-2 in which the in the bore hole.

4. A device according to claim 2 in which the resistances of two opposite arms of said bridge are arranged for direct heat exchange with the fluid in the bore hole.

5. An electrical circuit adapted to be lowered into a borehole filled with a drilling fluid at the end of a conductorcable and including afirst conductor carried by said cable, an electrical bridge comprising four arms, each containing an impedance, one of said impedances being a conductive element exposed to the fluid in the borehole and responsive to temperature changes in said fluid, means including said first conductor for supplying alternating current to two opposite Junctions of said bridge, means for rectifying alternating current into direct current electrically connected to the other two junctions of said bridge, and means including said first conductor for transmitting the rectified current from said rectifier to the surface.

6. A device for measuring temperature variations in a fluid in a borehole, comprising a bomblike casing attached to the end of a cable adapted to raise and lower said casing in the borehole, a first conductor carried by the said cable, an electrical bridge in said casing comprising four arms,

each containing an impedance, one of said impedances being a conductive element exposed to the fluid in the borehole and responsive to temperature changes in said fluid, means including said first conductor for supplying alternating current across two opposite junctions of said elec- J trical bridge, a rectifieiz-means electrically connected to the other two junctions of said bridge arranged to supply alternating current to said 'xrectifier, means arranged to conduct rectified cur- 

